1. Field of the Invention
The invention relates to a gear unit, in particular a gear unit with the features from the generic term of claim 1.
2. Description of the Related Art
Gear components are known in a large number of executions. These can be constructed as
a) mechanical gear unit
b) a hydrodynamic-mechanical compound gear unit.
Hydrodynamic-mechanical compound gear units are known, for example, from the following publications:
Buksch, M.: ZF five-gear automatic gears for passenger cars, VDI report 878 (1991).
Mitescu, G: Four-gear planetary gears for passenger automobiles with the hydrodynamic torque converter in the power branch. Automobilindustrie (1985) 5, pages 597-601.
Klement, W.: The development of the Voith-DIWA gears, Verkehr und Technik (1987) 7, pages 301-303.
The gear units which have either only purely mechanical transmission components or else that consist of a hydrodynamic coupling with a downstream mechanical gear set have, as a rule, a housing which with regard to its inner contour, is adapted to the formation and attachment to the housing of the individual gear elements and they have, as a rule, inner insets which undesirably reduce the inside diameter. The actuation of the individual switching arrangements occurs, as a rule, by pressure action over hydraulic pistons. For the resetting on releasing of the braking or coupling arrangements in these systems there is provided in each case either a large cup spring which is active on a piston, or a large number of individual pressure springs that are arranged on a carrier plate and again act on a piston. The pressure springs there, always viewed in radial direction, are arranged in a zone outside of the radial extent of the braking or coupling arrangements, or in the zone of the outer circumference they extend in axial direction into a zone which lies radially within the construction space prescribed by the coupling or braking arrangement. The supporting occurs there either on projections of the housing inner wall or, further the housing cover is used for the support in axial direction. This, however, has the disadvantage that by reason of the forces acting on the housing cover, a sealing-off is possible only with additional expenditure, and the housing cover likewise has to be secured in axial direction with respect to the rest of the gear housing. The basic gear then no longer be. can tested without housing cover but only in the installation state. Furthermore, angle drives are connectable only with difficulty to the gear output shaft since these, as a rule, likewise do not operate piston-free.
Underlying the invention, therefore, was the problem of developing a gear unit in which the disadvantages mentioned are avoided. In particular, the focus is to be set on a simpler housing formation as well as on a simple sealing and fastening of the housing cover to the gear housing. A testing of the gear is also to be possible when the housing is in the open state.
According to the invention the tying-on of the device for the resetting of the actuating elements, especially of the cylinder-piston arrangement as well as of individual gear elements into fixed position on the housing occurs by means of at least two means in the form of bar-form guide elements for the tying-on of gear elements in radial direction or in peripheral direction. These extend there essentially over a zone in which the gear elements provided for the tying-on are arranged. The bar-form guide elements are associated to the cylindrical interior space and are arranged in a zone outside of this, the allocation occurring in such manner that the bar-form guide elements are provided outside of this zone which, as viewed in installation position of the gear, corresponds to the greatest dimension of the cylindrical interior space of the gear unit in height direction.
Imperatively required are only two bar-form elements, but four are also possible. The arrangement occurs in this case as viewed in the cross section of the gear housing, in the corner zones, which is describable by the section size between the cylindrical interior space and a theoretically generatable quadrate with a side dimension greater than or equal to the diameter of the interior space, the theoretically generatable quadrate and the interior space having identical axes of symmetry. In this case, especially with a rectangular housing with cylindrical interior space,the material-intensive corner zones are used for the reception of the guide elements. The arrangement of the guide elements occurs thus outside of the middle vertical elements. The guide elements are guided there in recesses which are connected with the cylindrical interior space. Preferably, however, the arrangement of the guide elements always occurs symmetrically. This offers the advantage that the production expenditure for the gear elements and the gear housing can be minimized; furthermore this also applies to the assembling expenditure, since it is not necessary to heed how the individual recesses or passage openings have to be formed for the reception of the guide elements.
As gear elements there can be regarded, for example, braking arrangements in the form of lamellar brakes, partitions, actuating elements for braking or coupling arrangements, for example in the form of pistons, lamella carriers or the like.
The bar-form element s preferably have an equal or constant diameter over their axial extent. This offers the advantage that the assembling can occur independently from the installation direction of the bar-form elements. There is also conceivable, however, according to the formation of the total gear unit, the use of bar-form elements with different diameter over the axial extent. In this case, however, as a rule an assembling will occur from two side.
The cross section of the bar-form guide element is preferably circular. Also conceivable, however, are forms of execution with a quadrilateral cross section or an arbitrary cross section.
In respect to the bearing of the bar-form guide elements the following variants can be applied:
a) Bearing on the housing in housing wall projections
b) Bearing in partitions which are threaded onto the guide elements
c) Suspended bearing on a wall projection or a partition.
The gear unit can be constructed as a purely mechanical gear unit. In this case each bar-form guide element extends preferably over the entire axial extent of the gear component. In the execution of the gear unit as a hydrodynamic-mechanical compound gear unit, the bar-form guide elements are provided with an axial length which at least corresponds to the axial extent of the mechanical gear part with respect to the total gear unit. It is always necessary, however, that the axial extent of the guide elements corresponds to the axial extent of the gear elements to be supported on these.
These statements hold analogously also for the devices for the resetting of the actuating elements, of lamellar coupling and braking arrangements.
Between the two friction surface-carrying elements which are pressable on one another over a friction surface-carrying element, there is provided at least one spring storage arrangement which is likewise guided over the bar-form guide elements, and is designed in such manner that on generation of the frictional closure between the friction surface-carrying elements and the intermediate element the spring storage arrangement is pre-tensionable. The function of friction surface-carrying elements there can be taken over both by the outer as well as also by the inner lamellae. By reason of the action of the spring storage unit found between the individual friction surface-carrying elements, on relaxation of the actuating elements in each case a opposite force acts on the friction surface-carrying elements, so that a rapid separation becomes possible with complete releasing of the friction closure. The spring storage arrangements, therefore, act indirectly on the actuating element over the friction surface-carrying elements on the actuating element. The actuating element itself can be executed, for example, as a piston which can be acted upon hydraulically or pneumatically. This possibility of arranging the spring storage units between the friction surface-carrying elements offers the advantage that the dimensions of the friction surface-carrying elements in radial direction is no longer dependent on the size of the inner dimensions of the gear housing, with account taken of the necessary construction space for the device for the at least indirect resetting of actuating elements. The arrangement of spring storage units between the friction surface-carrying elements connectable with one another over an intermediate element offers also the advantage of a space-saving execution of the resetting device in axial direction, which again affects the gear length in use of the braking arrangements in lamellar construction in a gear. In regard to the arranging of the spring units between the friction surface-carrying elements a large number of possibilities are conceivable:
a) Arrangement of spring units between each of two adjacent friction surface-carrying elements;
b) Arrangement of the spring units in force flow direction between the friction surface-carrying elements in the zone of the force introduction (in the zone of the in each case outside-lying friction surface-carrying elements with respect to the installation position of the braking arrangement in a gear unit);
c) Arrangement of the spring unit between two adjacent friction surface-carrying elements with respect to the axial extent of the braking arrangement in the middle zone of these;
d) Arrangement according to b) in combination with c).
As spring storage units there are preferably used spring elements which have a characteristic-line characteristic with an essentially constant force flow over a certain spring path. Preferably, therefore, cup springs are used. The execution of the spring units as a shaft spring ring is likewise thinkable. The actuating arrangements used can be executed as cylinder-piston devices which can be acted upon hydraulically or pneumatically. According to the arrangement of the piston for the resetting device over the friction surface-carrying elements, lamellae on the piston are especially effective, either in the zone of the piston surface or outside of the piston surface. In respect to the formation of the piston there are distinguished forms of execution with
a) one piston
b) a plurality of pistons.
The appertaining cylinders there can be formed by one cylinder-carrying element or by a plurality of cylinder-carrying elements. This possibility of the piston resetting offers the advantage of a minimal space requirement in radial as well as in axial direction. In combination with the solution according to the invention there is given the possibility of creating a gear unit in which the torque transfer can take place with constant-remaining structural size, or with reduced structural size.